#include <iostream>
#include <vector>
#include <string>
int main(int argc, char *argv[])
{
  int n_test = 0;
  std::string dump;
  double time = 0;
  double total_time = 0;
  while(true)
    {
      if(!(std::cin >> dump))
	break;
      std::cin >> time;
      total_time += time;
      n_test++;
    }
  std::cout << total_time/n_test << std::endl;
  return 0;
};
